One type of pump assembly used particularly in oil producing wells has a submersible pump and electrical motor filled with a dielectric motor lubricant. The motor rotates a shaft assembly to drive the pump. A seal section connects between the motor and the pump. The seal section has a shaft seal to seal well fluid from contaminating the motor lubricant.
Normally, the shaft seal is a mechanical face seal having a rotating component or seal runner with an elastomeric boot mounted to the shaft for rotation with the shaft. A spring biases the seal runner against a stationary seal base. The interface between the seal runner and the seal base seals the well fluid from the motor lubricant.
The region of well fluid surrounding the upper portion of the mechanical face seal is relatively stagnant, although the rotation of the seal runner provides some disturbance to well fluid in this region. The rotational, sliding engagement of the seal runner with the seal base generates heat at the interface. Heat produced at the interface transfers through the head of the seal section and through the lubricant. In some installations, the heat transfer that occurs may be inadequate to cool the face seal to a desired temperature, thus decreasing the life.